The invention relates to an apparatus for delivering flat articles, such as sheets of paper and envelopes, one by one from a stack in a direction of transport.
Such apparatuses are used inter alia in so-called feeder stations for supplying such articles one by one. These feeder stations in turn can for instance be part of an insertion system for packaging the articles one by one in an envelope--optionally with associated articles supplied from other feeder stations.
A distinction can be made here between apparatuses of the clearance type and apparatuses of the contact type.
Apparatuses of the clearance type require accurate setting of the width of the clearance between the transport roller and the separation surface, which setting is moreover difficult to maintain, are complex in design and are not suitable for processing articles of mutually different thicknesses in a random order. When articles of widely varying thicknesses are to be processed in succession, adjustment of the width of the clearance moreover requires a great deal of time, because the setting means are designed for setting the clearance width with great precision. The width of the clearance therefore changes only very slowly when the setting means are operated.
U.S. Pat. Nos. 4,208,046 and 4,695,048 disclose apparatuses of the clearance type, in which a separation roller is resiliently pressed against a stop, so that it can spring away from the transport roller to allow passage of articles of a greater thickness than the width of the clearance. These apparatuses, too, however, require accurate setting of the width of the clearance, which is difficult to maintain, so as, on the one hand, to prevent contact between the transport roller and the separation surface and, on the other, to prevent a situation where two very thin sheets can pass the clearance simultaneously. Moreover, in such apparatuses it is problematic to introduce into the separation clearance articles of a greater thickness than the clearance width.
These drawbacks have been overcome in apparatuses of the contact type. Such apparatuses are known from German patent application 33 34 522 and U.S. Pat. No. 4,515,358. In these known apparatuses, the separation surface is designed as a circumferential surface of a separation roller which can be driven against the direction of transport. One of the rollers is suspended in a rocker which is held, by spring means, in a pivoted position disposed towards the opposite roller, so as to keep the roller which is suspended in the rocker pressed against the other roller with a substantially constant pressure force.
The operation of such an apparatus is based on the principle commonly referred to as `friction separation`, whereby, in the event of more than one article being passed between the transport roller and the separation surface, the articles not in contact with the transport roller are arrested through friction by the separation surface which is resiliently urged towards the transport roller. If the separation surface is designed as the circumferential surface of a separation roller which can be driven against the direction of transport, the articles not in contact with the transport roller can be passed back so as to prevent the separation surface from being covered by articles not in contact with the transport roller. However, it is also possible to design the separation surface to have a length in the direction of transport, such that in practice the separation surface will never be completely covered by entrained articles that are not in contact with the transport roller. The transport roller can be designed as a roller of a conveyor.
Advantages of apparatuses of the contact type over apparatuses of the clearance type are that it is not necessary to set the apparatus depending on the thickness of the articles to be processed and that a reliable processing of articles of mutually different thicknesses can be accomplished.
However, a drawback of apparatuses of the contact type is that they do not provide for a reliable processing of articles consisting of a plurality of layers which are fixed relative to each other to a limited extent, such as folded sheets or a set of loose documents to be processed into a postal item, in particular when the layers of these articles have minor stiffness. As such articles are being processed, the layers thereof are shifted at least partly relative to each other, which prevents further processing. If the layers are connected to each other along one or more folding or binding edges, the layers may moreover fold, crease, tear and get stuck in the machine. This problem, for that matter, also presents itself in the clearance type apparatuses described above, where the separation roller is resiliently pressed against a stop.